Installations for the printing of containers are used above all in the industrial sector. An installation of this type is described by way of example in DE 10 2009 058 219 A1. This installation, for the printing of containers, has a plurality of printing machines connected in series which are formed as a carousel, through which machines the containers to be printed are passed via a transport system constructed from various systems, such as chucking device, transport devices and holding means. The containers are moved in each carousel past the print heads of the printing machines and thus are provided with a printed pattern before being transferred into the subsequent carousel. After passing through the installation, the containers are provided with the desired motif. Of course, installations with only one printing machine, in particular one in the form of a carousel printing machine, are also known, and the invention equally relates to these.
When these installations are used on an industrial level, above all a high throughput rate is a factor relevant to competition. By way of example at this point we mention an installation for processing bottles in which up to 36,000 bottles per hour are passed through the installation. Within the installation, the bottles are guided past print heads of the printing machine and in so doing are printed with liquid printing inks via the inkjet print heads.
Printing machines for inkjet printers within such installations as a rule operate with one or more print heads having a plurality of nozzles. In this case, approximately 1000 of said nozzles are arranged in a row on the print head in order to obtain the desired resolution in the region to be printed. Since especially in industrial use a high throughput rate with high and permanent print quality is required, efficient maintenance and cleaning of the print heads is also necessary. Experience shows that the print heads become soiled due to the continuous operation required by the type of application. Thus for example dust and ink deposits may soil the nozzles. These problems are intensified when using UV-curing inks if the printed container after printing is irradiated with UV light while still in the printing machine to fix the printed-on ink. Scattered UV light can also cure the ink which is still in the nozzles and make the print head unusable if it is not cleaned regularly and effectively.
In order to maintain the functionality and print quality of the print heads, a print head therefore has to be cleaned at certain intervals. Several cleaning methods which are known in principle are available for this purpose. A first possible way is to wipe off the soiling from the print head by means of a stripper or the like in the manner of mechanical cleaning. A system which operates in such a manner is described for example in US 2003/0218654 A1. Here, a print head, for the purpose of cleaning, is moved from its operating region into a maintenance region in which a cleaning device of a wiper unit with a type of windscreen wiper moves along the underside of the print head with the nozzles, so that residues of the printing liquid are removed by the stripper or wiper. After cleaning, the print head is moved back into its operating region.
What is problematic here, however, is that the cleaning system involves an increased space requirement. Furthermore, the cleaning operation is complex owing to the moving of the print head, because a corresponding adjustment means is provided which in addition has to ensure very reliable and precise repositioning so that the print quality is not adversely affected. In addition, moving the print head into the cleaning position has an adverse effect on the throughput of the entire installation, because the print head cannot be used for a considerable period of time within the installation.
One further known possibility for cleaning a print head consists of flushing the print head through. Cleaning and flushing solutions may be used here. Also all the nozzles can be controlled, optionally even multiply, so that those nozzles which are seldom used are also flushed through. In this case, flushing may also take place with the ink actually used for printing. In both cases, it is however necessary to collect the emerging liquid and dispose of it specifically. However, in particular if the nozzles are flushed through under pressure, the immediate surroundings of the print head, for example other print heads, may also be soiled by ink, or splashes of cleaning agent or the like which are contaminated with ink. Also an ink mist may occur which is deposited at unwanted points.
DE 10 2006 052 154 A1 describes a cleaning device for the cleaning of inkjet printers in which the print head is cleaned as described previously. The ink ejected from the inkjet print head during the cleaning operation is collected in a collecting container. For this, the print head to be cleaned is moved out of its operating position into a maintenance and cleaning position. Then the print head is flushed for a certain time by means of excess pressure in the ink system, so that ink flows out of all the nozzles at the same time and dust or dirt particles, and also cured ink residues, are flushed away. A lamella arrangement on the collecting device collects the dirt and guides it into the collecting container.
Here too, the problem linked to the disadvantages already described exists, namely that the print head cannot be used for a comparatively long period of time and has to be moved out of its operating position into a cleaning position.
A printer device and a method for printing on a print medium with a print head and a transport device for the print medium are known from U.S. Pat. No. 6,182,566 B1. Therein, the print head is not moved during printing, but the print medium is moved relative to the print head by a transport means and a displacement means. For cleaning, the print head is pivoted about an axis into a predetermined position to a cleaning and sealing station.
A printing apparatus for the printing of bottles or similar containers is known from US 2011/232514 A1. This has a plurality of printing positions on a transport element which can be driven in rotation, with which the printing position and the containers are moved on a closed path of movement from a container charge station to a container removal station. In order to avoid soiling of the print heads, a protective sleeve is provided which surrounds the container to be printed during printing. During printing, when the protective sleeve is closed an air stream is generated through the protective sleeve, and atomised printing ink is removed by extraction tubes.